Node and Host Name Sizes on HP-UX: Using the Expanded Capabilities of HP-UX

Debuggers

The debugger does not have access to source names. It has access only to the binary names. Thus,

displays (such as stack traces) provide binary names. When looking up functions or data, the binary

name must be supplied. Note also that a breakpoint set in one version of a function does not affect

calls to another version.

Assembly and Fortran: No Version

The assembler and the Fortran language ignore the version attributes. The binary names are the

same as the source names. These languages always reference the original version of an interface

unless the source code is modified explicitly to use the binary name.

Incomplete Types

A pointer to an incomplete type might be used in another type (for example, as a structure member or

function parameter). If the referenced type has a version identifier, that version identifier might not

propagate to the pointer type or to any interfaces that use it. The workaround is to provide the

complete type or apply a version identifier directly to the pointer.

Type Casts

Type casts in a program source might be used to cast a pointer to the wrong version of a type. The

compiler checking scheme might fail to detect a mismatch or might diagnose false mismatches.

Extensive Use of Interfaces

If an interface is versioned that is used by the majority of client applications, or if many interfaces are

versioned (perhaps through version inheritance), it can become impossible for client programs to

effectively use the original interface versions. All client applications are, for practical matters, forced

into using the new versioned interfaces. In this case, it is more appropriate to require recompilation

of all client programs (with possible source code updates) to use the new versions of the interfaces

and to not use FLV at all.

Versioning is Cumulative

Interfaces cannot be versioned independently; versions must be cumulative. A client application

cannot individually pick which versions are used for each interface it uses. This constraint is due to

the fact that structures or functions that re-export multiple versioned interfaces inherit the version

identifier that is lexically greatest (the high-water mark).

Virtual Member Functions and Derived Classes

If a base class is recompiled with a new version identifier but the derived class is not, a call to that

function on an instance of the derived class might not work properly. This situation is really a general

C++ binary compatibility issue and can occur even in the absence of the FLV mechanism.

Defeats Single-Binary/Multiple-Release

Many software developers build their products on an earlier HP-UX release (for example, 11.00 or

11i versions 1.0, 1.5, 1.6) and deploy the single binary on that and all later releases and versions.

The FLV mechanisms cannot be retrofitted to those releases. The same is true for the versioned

interfaces themselves. Furthermore, because FLV is a compile-time feature, it is not straightforward to

make run-time decisions about whether to use the original or new interfaces. So run-time conditional

execution is not practical.